a) Field of the Invention
The present invention relates to compositions useful as lubricating oil.
b) Description of the Related Art
With respect to the applicational field of the lubricating oil compositions, the recent technical situation and the technical subject which is required to solve, will firstly be described.
Various types of refrigerating machines have heretofore been used. In these refrigerating machines, refrigerating machines which are effected by compressing the vapor of a refrigerant are classified into three types composed of rotary compressor type, reciprocating compressor type and centrifugal compressor type, in accordance with structural type of their compressors.
The rotary refrigerating machines, namely refrigerating machines having a rotary compressor, are widely employed to refrigerators, air conditioners and the like for home use, because they have such a meritorious property that they can be miniaturized and driven with a highly reduced noise.
On the other hand, the reciprocative refrigerating machines are also widely employed as refrigerating machines for car air conditioners and the like, because they can be made as a big one having a large refrigerating capacity and have high mechanical reliability.
As the refrigerants for the refrigerating machines having a type of compressing the vapor of the refrigerant, there are widely used halogenated hydrocarbons typified by trichloromonofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), monochlorodifluoromethane (HCFC-22), trichlorotrifluoroethane (CFC-113) or the like, hydrocarbons, in which propane is a typical substance, and inorganic gases typified by ammonia, carbon dioxide or the like.
In addition, it has recently been known that 1,1,1,2-tetrafluoroethane (HFC-134a) is also useful as a refrigerant alternative to CFC-12, for avoiding the destruction of the ozone layer in the high altitude atmosphere due to the conventional refrigerants of CFC type.
As lubricating oils for the refrigerating machines using such refrigerants, there are generally used paraffinic mineral oils, naphthenic mineral oils, alkylbenzenes, poly-.alpha.-olefines, oils consisting of polyoxyalkylene and/or polyalkylene glycol compounds and a mixture of two or more of these oils, or oils obtained by adding one or more additives to these base oils.
As such additives, there are mainly used antioxidants of phenolic or amino compounds, compounds of benzotriazole type for inactivating metals (Japanese Patent Publication 19352/1985), hydrogen chloride removing agents typified by epoxy compounds (Japanese Patent Publication 42119/1982), load carrying additives of esterified compounds of phosphoric acid typified by triphenyl phosphate and tricresyl phosphate.
The refrigerating machines which are effected by compressing the vapor of the refrigerant under the use of such a lubricating oil, are continuously operated for a very long period of time as refrigerating machines in refrigerators, or are intermittently operated under rigorous conditions as refrigerating machines in car air conditioners accompanied by a high load and the repeated and sudden changes between their stopped state and operated state. Therefore, they must have a high grade safety and reliability in their operations.
According to the recently strengthened tendency of demanding the miniaturization and lightening with regard to almost every kinds of machines, the refrigerating machine have also been forced so as to operate under more rigorous conditions caused by its miniaturized and lightened design.
As a matter of course, the wear resistant properties of the metal portions contacting and sliding each other in such refrigerating machines are very important. For example, when the top ends of the vanes of the rotor or the inner surface of the compressor housing in a rotary compressor are worn, the vapor of the refrigerant leaks through the gap generated between the vane and the housing by the abrasion, and as the result, the compression efficiency of the compressor is reduced. Moreover, when the wear proceeded to an extreme state, the compressor can not continue its mechanically smooth operation, and finaly it becomes entirely impossible to operate by the reason of co-searing phenomenon of the metal portions to be smoothly slided each other.
Conventional lubricating oils become insufficient for giving enough wear resistant properties to the sliding metal portions of the compressor which is designed in accordance with the recent tendency of miniaturizing and lightening the refrigerating machines and is driven under more rigorous operating conditions than those of conventional one.
Additionally, with regard to the lubricating oils for metal processing which is an important application field of lubricating oils, although esters of phosphorous acid which have heretofore been used as extreme pressure agents can increase the lubricational properties of the metal processing oil, the esters have problems in their stabilities such as storage stability, thermal stability and stability for hydrolysis. The shortage in these stabilities can be improved by adding an amine compound to the oil. However, the lubricational properties of the metal processing oil is inversely reduced by the addition of such an amine compound.
Further, phosphate esters and zinc dithiophosphate as the alternatives of the esters of phosphorous acid are excellent in the stabilities, however such alternatives can not give any satisfactory metal processing oil having sufficient lubricational properties.